A Grolar Bear? The Perils of Shrinking Arctic Ice

Shrinking ice sheets in the Arctic Ocean could be promoting breeding between different species, creating hybrid whales and bears, according to a paper published on Thursday in the journal Nature.

As global temperatures rise, scientists have noted that sea ice in the Arctic is getting thinner. They expect that by midcentury, a passage through the ice sheet will be available for at least one month each summer.

A paper by a trio of researchers explores what the loss of this nearly-continent-size barrier could mean for species inhabiting the region. The paper lists 22 species that are at risk of hybridization, including the narwhal and the polar bear. Of those, about 14 are threatened or will soon be threatened. They say that such interbreeding between such species is already occurring — an animal that was a mix of grizzly bear and polar bear was found in 2006, for example — and will probably increase.

The long-term results could be devastating because the genes of many of these species developed over millenniums in isolated populations, giving these Arctic marine animals sets of fine-tuned adaptations that helping them uniquely thrive in the harsh environment, the researchers write.

The paper was authored by Brendan Kelly, a marine mammalogist with the National Oceanic and Atmospheric Administration’s marine mammal lab in Juneau, Alaska; Andrew Whiteley, a conservation geneticist at the University of Massachusetts at Amherst; and David Tallmon, an evolutionary biologist at the University of Alaska.

Normally, species have pre-mating isolating mechanisms in place, Dr. Whiteley said. “Signals the animals use could be behavioral — for example, bird songs — or morphological, maybe related to bright colors,” he said.

When species have evolved together, these isolating mechanisms are advantageous because hybrids tend to lose out in natural selection. “However, if species have evolved in separate habitats and in isolation from each other, they tend to lose these isolating mechanisms,” he said.

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